Awesome Gary, glad the book helped make a bit more sense of the CTX for you.
Ok, if stock standard there is no screen protection. I made my own by cutting a piece of "Zagg Invisible Shield", it's tricky to get it right but not that hard, just follow the instructions.
One quirk with the depth function is it will say a $1 or $2 coin will register at 5cm but still be on the surface. If you get any target that says it's less than 5cm it will usually be large junk but not always, check it out to make sure. To answer your question though would be yes, the higher the coil is above the ground the deeper it will say the target is sitting.
Not sure about the digging tool mate, in my area I could probably get in trouble for carrying it but I sort of see it a bit like fishing, you sort of need a knife. Really can't help you with that one, though any reasonable officer would see that it's digging tool and not a knife and a warning would be hopefully all you got or not even a warning especially if your not being offensive with it.
I usuallu use the standard coin mode, I have made copies of that and modified settings for my own use, I have also made my own programs from scratch too such as my own Aussie Silver program and goldies program. All the programs in the CTX have the same parameters but are just different adjustments/settings of those parameters and also of course different discrimination patterns, they are in essence just all presets for switch on and go detecting for different scenarios that can be user tweaked for fine tuning.
I always use the pinpoint function when narrowing down a target, it works great, and then use my small pinpointer too for minimal ground disturbance. With the pinpointing too, switch on pinpoint trace and target trace too, that gives you the visual on the screen, these should be on by default but aren't.
Bank account details are fine to use such as BSB and account numbers, keep always your password to yourself though.
All the best with it mate lookimng forward to seeing what you find with it.
Hope this helps mate. Anymore questions just pop them in here, I'll be happy to help out.